Aerosol-generating element comprising a filter with a high content of a polyhydroxyalkanoate polymer or copolymer

ABSTRACT

An aerosol-generating article is provided for producing an inhalable aerosol upon heating, the aerosol-generating article including: a rod of aerosol-generating substrate, the aerosol-generating substrate including at least 10 percent by weight of an aerosol former; and a filter segment formed of fibrous filtration material, the filter segment arranged in longitudinal alignment with the rod, in which the filter segment includes at least about 85 percent by weight based on a total weight of fibrous filtration material of a polyhydroxyalkanoate (PHA) polymer or copolymer, in which a resistance to draw (RTD) of the filter segment is between about 35 millimetres H2O and about 55 millimetres H2O, and in which a length of the filter segment is from about 4 millimetres to about 27 millimetres. A filter for an aerosol-generating article is also provided.

The present invention relates to a filter for an aerosol-generatingarticle and to an aerosol-generating article comprising the filter. Thepresent invention further relates to an aerosol-generating systemcomprising an aerosol-generating device and one such aerosol-generatingarticle.

Conventional aerosol-generating articles, such as filter cigarettes,typically comprise a cylindrical rod of tobacco cut filler surrounded bya paper wrapper and a cylindrical filter axially aligned, most often inan abutting end-to-end relationship, with the wrapped tobacco rod. Thecylindrical filter typically comprises one or more plugs of a fibrousfiltration material, such as cellulose acetate tow, circumscribed by apaper plug wrap. Conventionally, the wrapped tobacco rod and the filterare joined by a band of tipping wrapper, normally formed of an opaquepaper material that circumscribes the entire length of the filter and anadjacent portion of the wrapped tobacco rod.

Aerosol-generating articles in which an aerosol-generating substrate,such as a tobacco-containing substrate, is heated rather than combusted,are also known in the art. Typically in such articles an aerosol isgenerated by the transfer of heat from a heat source to a physicallyseparate aerosol-generating substrate or material.

By way of example, aerosol-generating articles have been proposedwherein an aerosol is generated by electrical heating of anaerosol-generating substrate. A number of prior art documents discloseaerosol-generating devices for consuming aerosol-generating articles.Such devices include, for example, electrically heatedaerosol-generating devices in which an aerosol is generated by thetransfer of heat from one or more electrical heater elements of theaerosol-generating device to the aerosol-generating substrate of aheated aerosol-generating article. As another example,aerosol-generating articles are also known wherein an aerosol isgenerated by the transfer of heat from a combustible fuel element orheat source to an aerosol-generating substrate. The combustible fuelelement or heat source may be located in contact with, within, around,or downstream of the aerosol-generating substrate.

During use of one such aerosol-generating article, volatile compoundsare released from the aerosol-generating substrate by heat transfer andare entrained in air drawn through the aerosol-generating article. Asthe released compounds cool, they condense to form an aerosol.

Typically, aerosol-generating articles of the types described mayinclude a mouthpiece comprising a filter segment formed of porousfiltration material such as cellulose acetate. In some knownaerosol-generating articles a hollow tubular segment formed of afiltration material such as cellulose acetate is provided at a locationbetween the aerosol-generating substrate and the mouth end of thearticle to impart structural strength to the article.

After an aerosol-generating article has been consumed and discarded, itmay be desirable for any component of the article comprising filtrationmaterial to break down as quickly as possible. However, celluloseacetate, and many other commonly used filtration materials are nothighly biodegradable. However, alternative dispersible or biodegradablematerials are often not able to provide an acceptable filtrationefficiency and smoking experience for the consumer. Furthermore, manyknown dispersible and degradable materials are unsuitable for use in theexisting manufacturing processes, and would require too significant amodification of the existing methods and equipment to make their usecommercially feasible.

Further, cellulose acetate has been found to provide a relatively highlevel of adsorption and trapping of water from the mainstream smoke whenused in conventional smoking articles. The mainstream smoke delivered tothe consumer therefore has a significantly reduced moisture content andmay, under certain conditions, be perceived as undesirably ‘dry’. Thismay have an adverse effect on the overall smoking experience.

Thus, it would be desirable to provide a novel and improvedaerosol-generating article that has enhanced biodegradation propertiescompared to known articles including conventional filtration materialssuch as cellulose acetate. It would also be desirable to provide a noveland improved aerosol-generating article that provides an acceptablesmoking experience to the consumer, in particular, one that is capableof reducing the ‘dry’ smoke effect that is often found with articlescomprising cellulose acetate as the filtration material.

It would be desirable to provide one such aerosol-generating articlewherein the resistance to draw (RTD) of a filtration material segmentcan be adjusted so as to achieve an acceptable RTD of the article as awhole. Further, it would be desirable to provide such anaerosol—generating article that can effectively be produced in anautomated, high-speed manufacturing process without requiring majormodifications of existing equipment.

The present disclosure relates to an aerosol-generating article forproducing an inhalable aerosol upon heating. The aerosol-generatingarticle may comprise a rod of aerosol-generating substrate and a filtersegment formed of fibrous filtration material. The filter segment may bearranged in longitudinal alignment with the rod. The filter segment maycomprise at least about 85 percent by weight based on the total weightof fibrous filtration material of a polyhydroxyalkanoate (PHA) polymeror copolymer.

Further, the present disclosure relates to a filter for anaerosol-generating article. The filter may comprise a filter segmentformed of fibrous filtration material. The filter segment may compriseat least about 85 percent by weight based on the total weight of fibrousfiltration material of fibres comprising a polyhydroxyalkanoate PHApolymer or copolymer.

In addition, the present disclosure relates to a system comprising anaerosol-generating device and an aerosol-generating article for use withthe aerosol-generating device. The aerosol-generating article maycomprise a rod of aerosol-generating substrate and a filter segmentformed of fibrous filtration material. The filter segment may bearranged in longitudinal alignment with the rod. The filter segment maycomprise at least about 85 percent by weight based on the total weightof fibrous filtration material of a polyhydroxyalkanoate (PHA) polymeror copolymer.

According to the present invention, there is provided anaerosol-generating article for producing an inhalable aerosol uponheating, the aerosol-generating article comprising: a rod ofaerosol-generating substrate; a filter segment formed of fibrousfiltration material, the filter segment arranged in longitudinalalignment with the rod; wherein the filter segment comprises at leastabout 85 percent by weight based on the total weight of fibrousfiltration material of a PHA polymer or copolymer.

According to the present invention, there is also provided a filter foran aerosol-generating article, the filter comprising a filter segmentformed of fibrous filtration material, wherein the filter segmentcomprises at least about 85 percent by weight based on the total weightof fibrous filtration material of a PHA polymer or copolymer.

As used herein, the term “longitudinal” refers to the directioncorresponding to the main longitudinal axis of the aerosol-generatingarticle, which extends between the upstream and downstream ends of theaerosol-generating article. As used herein, the terms “upstream” and“downstream” describe the relative positions of elements, or portions ofelements, of the aerosol-generating article in relation to the directionin which the aerosol is transported through the aerosol-generatingarticle during use.

The term “aerosol-generating article” is used herein with reference tothe invention to describe an article wherein an aerosol-generatingsubstrate is heated to produce and deliver an aerosol to a consumer. Asused herein, the term “aerosol-generating substrate” denotes a substratecapable of releasing volatile compounds upon heating to generate anaerosol.

A conventional cigarette is lit when a user applies a flame to one endof the cigarette and draws air through the other end. The localised heatprovided by the flame and the oxygen in the air drawn through thecigarette causes the end of the cigarette to ignite, and the resultingcombustion generates an inhalable smoke. By contrast, in heatedaerosol-generating articles, an aerosol is generated by heating aflavour generating substrate, such as, for example, a tobacco-basedsubstrate or a substrate containing an aerosol-former and a flavouring.Known heated aerosol-generating articles include, for example,electrically heated aerosol-generating articles and aerosol-generatingarticles in which an aerosol is generated by the transfer of heat from acombustible fuel element or heat source to a physically separate aerosolforming material.

As described briefly above, in contrast with existing aerosol-generatingarticles, an article in accordance with the present invention comprisesa filter segment formed of fibrous filtration material and comprising atleast about 85 percent by weight based on the total weight of thefibrous filtration material of a PHA polymer or copolymer.

Thus, in the filter segment of an aerosol-generating article inaccordance with the invention a PHA polymer or copolymer accounts for atleast 85 percent by weight of the fibrous filtration material. Thismeans that the remainder of the fibrous filtration material may comprisea material other than a PHA polymer or copolymer. Further, this meansthat other components of the filter segment—such as, for example, a plugwrapper circumscribing the fibrous filtration material, or an insertsuch as a flow restrictor or an additive delivery material, for examplea breakable capsule, which may be provided at a location in the filtersegment may comprise a material other than a PHA polymer or copolymer.

Because fibres containing a PHA polymer or copolymer (in the following,also referred to as “PHA fibres”) have a lower hydrophilicity comparedwith fibres of other filtration materials, such as cellulose acetate, ofan equivalent weight, in aerosol-generating articles in accordance withthe present invention the filter segment has been found to have asignificantly lower tendency to absorb water/steam. As a result, thelevel of water in the mainstream smoke can advantageously be maintainedat a higher level. This directly addresses the issue of “dry smoke”often encountered with conventional smoking articles, and provides animproved smoking experience for the consumer.

As PHA fibres have a much higher level of biodegradability compared withfibres of other filtration materials, such as cellulose acetate,articles in accordance with the present invention are more biodegradableas a whole. At the same time, as PHA fibres are obtained by means of anatural, fermentation process, aerosol-generating articles in accordancewith the present invention also provide improved sustainability for theproduction process.

By adjusting parameters such as the denier per filament, total denier,cross sectional shape, etc. it is possible to adjust the RTD of thefilter segment to desirable ranges for any given filter length or filterdesign.

The term “denier per filament” (DPF) corresponds to the weight in gramsof a single fibre or filament having a length of 9000 metres. In thepresent invention, the value of DPF therefore gives an indication of thethickness of each of the individual PHA fibres within the filtersegment. The denier per filament is expressed in units of denier, where1 denier corresponds to 1 gram per 9000 metres.

Preferably, the total denier of the filtration material comprising thePHA fibres is between about 20,000 and about 50,000 or 40,000, morepreferably between about 25,000 and about 30,000.

The “total denier” of the filtration material defines the total weightin grams of 9000 metres of the combined fibres forming the filtrationmaterial. The total denier for the filter segment therefore correspondsto the denier per filament multiplied by the total number of fibres inthe filter segment.

In addition, the overall weight of the filter may be advantageouslycontrolled, and this may also contribute to help with biodegradation ofthe filter segment and of the aerosol-generating article as a whole.

PHA properties also lead to good filter hardness, which can be furtherenhanced by circumscribing the filter segment with a stiff plug wrap.

Aerosol-generating articles in accordance with the present inventioncomprise a rod of aerosol-generating substrate.

The rod of aerosol-generating substrate may be produced using randomlyoriented shreds, strands, or strips of tobacco material. As analternative, as has been proposed, for example in international patentapplication WO-A-2012/164009, the rod of aerosol-generating substratemay be formed from one or more gathered sheets of tobacco material.Alternative rods for aerosol-generating articles have also been proposedthat are formed from strands of homogenised tobacco material, which maybe formed by casting, rolling, calendering or extruding a mixturecomprising particulate tobacco and at least one aerosol former to form asheet of homogenised tobacco material. Further, a rod ofaerosol-generating substrate may be formed from strands of homogenisedtobacco material obtained by extruding a mixture comprising particulatetobacco and at least one aerosol former to form continuous lengths ofhomogenised tobacco material.

The rod of aerosol generating substrate preferably has an externaldiameter that is approximately equal to the external diameter of theaerosol generating article.

Preferably, the rod of aerosol generating substrate has an externaldiameter of at least 5 millimetres. The rod of aerosol generatingsubstrate may have an external diameter of between about 5 millimetresand about 12 millimetres, for example of between about 5 millimetres andabout 10 millimetres or of between about 6 millimetres and about 8millimetres. In a preferred embodiment, the rod of aerosol generatingsubstrate has an external diameter of 7.2 millimetres, to within 10percent.

The rod of aerosol generating substrate may have a length of betweenabout 5 millimetres and about 100 mm. Preferably, the rod of aerosolgenerating substrate has a length of at least about 5 millimetres, morepreferably at least about 7 millimetres. In addition, or as analternative, the rod of aerosol generating substrate preferably has alength of less than about 80 millimetres, more preferably less thanabout 65 millimetres, even more preferably less than about 50millimetres. In particularly preferred embodiments, the rod of aerosolgenerating substrate has a length of less than about 35 millimetres,more preferably less than 25 millimetres, even more preferably less thanabout 20 millimetres. In one embodiment, the rod of aerosol generatingsubstrate may have a length of about 10 millimetres. In a preferredembodiment, the rod of aerosol generating substrate has a length ofabout 12 millimetres.

Preferably, the rod of aerosol generating substrate has a substantiallyuniform cross-section along the length of the rod. Particularlypreferably, the rod of aerosol generating substrate has a substantiallycircular cross-section.

In preferred embodiments, the aerosol-generating substrate comprises oneor more gathered sheets of homogenised tobacco material. Preferably theone or more sheets of homogenised tobacco material are textured. As usedherein, the term ‘textured sheet’ denotes a sheet that has been crimped,embossed, debossed, perforated or otherwise deformed. Textured sheets ofhomogenised tobacco material for use in the invention may comprise aplurality of spaced-apart indentations, protrusions, perforations or acombination thereof. According to a particularly preferred embodiment ofthe invention, the rod of aerosol-generating substrate comprises agathered crimped sheet of homogenised tobacco material circumscribed bya wrapper.

As used herein, the term ‘crimped sheet’ is intended to be synonymouswith the term ‘creped sheet’ and denotes a sheet having a plurality ofsubstantially parallel ridges or corrugations. Preferably, the crimpedsheet of homogenised tobacco material has a plurality of ridges orcorrugations substantially parallel to the cylindrical axis of the rodaccording to the invention. This advantageously facilitates gathering ofthe crimped sheet of homogenised tobacco material to form the rod.However, it will be appreciated that crimped sheets of homogenisedtobacco material for use in the invention may alternatively or inaddition have a plurality of substantially parallel ridges orcorrugations disposed at an acute or obtuse angle to the cylindricalaxis of the rod. In certain embodiments, sheets of homogenised tobaccomaterial for use in the rod of the article of the invention may besubstantially evenly textured over substantially their entire surface.For example, crimped sheets of homogenised tobacco material for use inthe manufacture of a rod for use in an aerosol-generating article inaccordance with the invention may comprise a plurality of substantiallyparallel ridges or corrugations that are substantially evenlyspaced-apart across the width of the sheet.

Sheets or webs of homogenised tobacco material for use in the inventionmay have a tobacco content of at least about 40 percent by weight on adry weight basis, more preferably of at least about 60 percent by weighton a dry weight basis, more preferably or at least about 70 percent byweight on a dry basis and most preferably at least about 90 percent byweight on a dry weight basis.

Sheets or webs of homogenised tobacco material for use in theaerosol-generating substrate may comprise one or more intrinsic binders,that is tobacco endogenous binders, one or more extrinsic binders, thatis tobacco exogenous binders, or a combination thereof to helpagglomerate the particulate tobacco. Alternatively, or in addition,sheets of homogenised tobacco material for use in the aerosol-generatingsubstrate may comprise other additives including, but not limited to,tobacco and non-tobacco fibres, aerosol-formers, humectants,plasticisers, flavourants, fillers, aqueous and non-aqueous solvents andcombinations thereof.

Suitable extrinsic binders for inclusion in sheets or webs ofhomogenised tobacco material for use in the aerosol-generating substrateare known in the art and include, but are not limited to: gums such as,for example, guar gum, xanthan gum, arabic gum and locust bean gum;cellulosic binders such as, for example, hydroxypropyl cellulose,carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose andethyl cellulose; polysaccharides such as, for example, starches, organicacids, such as alginic acid, conjugate base salts of organic acids, suchas sodium-alginate, agar and pectins; and combinations thereof.

Suitable non-tobacco fibres for inclusion in sheets or webs ofhomogenised tobacco material for use in the aerosol-generating substrateare known in the art and include, but are not limited to: cellulosefibres; soft-wood fibres; hard-wood fibres; jute fibres and combinationsthereof. Prior to inclusion in sheets of homogenised tobacco materialfor use in the aerosol-generating substrate, non-tobacco fibres may betreated by suitable processes known in the art including, but notlimited to: mechanical pulping; refining; chemical pulping; bleaching;sulphate pulping; and combinations thereof.

Substrates for heated aerosol-generating articles typically comprise an“aerosol former”, that is, a compound or mixture of compounds that, inuse, facilitates formation of the aerosol, and that preferably issubstantially resistant to thermal degradation at the operatingtemperature of the aerosol-generating article. Examples of suitableaerosol-formers include: polyhydric alcohols, such as propylene glycol,triethylene glycol, 1,3-butanediol and glycerin; esters of polyhydricalcohols, such as glycerol mono-, di- or triacetate; and aliphaticesters of mono-, di- or polycarboxylic acids, such as dimethyldodecanedioate and dimethyl tetradecanedioate. Preferred aerosol formersare polyhydric alcohols or mixtures thereof, such as propylene glycol,triethylene glycol, 1,3-butanediol and, most preferred, glycerine.

Preferably, the aerosol-generating substrate comprises at least 10percent by weight of an aerosol former, more preferably at least 12percent by weight of an aerosol former, more preferably at least about15 percent by weight of an aerosol former. Alternatively or in addition,the aerosol-generating substrate preferably comprises no more than 30percent by weight of an aerosol former, more preferably no more thanabout 25 percent by weight of an aerosol former, more preferably no morethan about 20 percent by weight of an aerosol former. For example, theaerosol-generating substrate may comprise between about 10 percent andabout 30 percent by weight of an aerosol former, or between about 12percent and about 25 percent by weight of an aerosol former, or betweenabout 15 percent and about 20 percent by weight of an aerosol former. Ina particularly preferred embodiment, the aerosol-generating substratecomprises around 18 percent by weight of an aerosol former.

In aerosol-generating articles in accordance with the present invention,the filter segment is formed of fibrous filtration material andcomprises at least 85 percent by weight of a PHA polymer or copolymerbased on the total weight of the fibrous filtration material.

PHAs are a family of polyhydroxyesters of 3-, 4-, 5- and6-hydroxyalkanoic acids, which are produced by a variety of bacterialspecies under nutrient-limiting conditions with excess carbon and arefound as discrete cytoplasmic inclusions in bacterial cells. Due totheir excellent biocompatibility, PHAs have been proposed for use in awide variety of biomedical applications, including drug delivery systemsand tissue engineering scaffolds.

A PHA molecule is typically made up of 600 to 35,000 (R)-hydroxy fattyacid monomer units. Depending on the total number of carbon atoms withina PHA monomer, PHA can be classified as either short-chain length PHA(scl-PHA; 3 to 5 carbon atoms), medium-chain length PHA (mcl-PHA; 6 to14 carbon atoms), or long-chain length PHA (lcl-PHA; 15 or more carbonatoms).

The first and most prevalent PHA is poly(β-hydroxybutyrate) (PHB). Thenext member of the PHA family, having a pendant ethyl group, ispoly(3-hydroxyvalerate) or PHV. Having an ethyl group (HV unit) insteadof the methyl group of PHB gives PHV more flexibility and lesscrystallinity than PHB.

The PHA-containing fibres provided within the filter segment of theaerosol-generating articles according to the invention may be formed ofany suitable PHA compound, including PHA polymers or copolymers.Suitable PHA compounds include but are not limited to:polyhydroxypropionate, polyhydroxyvalerate, polyhydroxybutyrate,polyhydroxyhexanoate and polyhydroxyoctanoate. In a particularlypreferred embodiment, the PHA compound is poly(3-hydroxybutyrate).

Preferably, in an aerosol-generating article in accordance with theinvention the filter segment comprises at least 85 percent by weight ofa PHA polymer or copolymer. Without wishing to be bound by theory, it isunderstood that higher contents of PHA in the filter segment aregenerally associated with an improved biodegradability of the filtersegment and of the aerosol-generating article as a whole.

In preferred embodiments, the filter segment comprises at least about 90percent by weight of a PHA polymer or copolymer. Without wishing to bebound by theory, it is understood that higher contents of PHA in thefilter segment are generally associated with an improvedbiodegradability of the filter segment and of the aerosol-generatingarticle as a whole.

More preferably, the filter segment comprises at least about 91 percentby weight of a PHA polymer or copolymer or at least about 92 percent byweight of a PHA polymer or copolymer or at least about 93 percent byweight of a PHA polymer or copolymer or at least about 94 percent byweight of a PHA polymer or copolymer. In some particularly preferredembodiments, the filter segment comprises at least about 95 percent byweight of a PHA polymer or copolymer.

The remainder of the fibres within the PHA filter segment may compriseany suitable material. Suitable fibrous materials would be known to theskilled person and include but are not limited to polylactic acid (PLA)and cellulose acetate.

In some embodiments, the filter segment may comprise some celluloseacetate. Without wishing to be bound by theory, it is understood that acertain amount of cellulose acetate in the filter segment may impartdesirable filtration properties and mechanical properties to the filtersegment as well as facilitating manufacture of the filter segment.

In certain embodiments, the filter segment comprises at least about 5percent by weight of cellulose acetate. By way of example, the filtersegment may comprise at least about 6 percent by weight of celluloseacetate or at least about 7 percent by weight of cellulose acetate or atleast about 8 percent by weight of cellulose acetate or at least about 9percent by weight of cellulose acetate. In some embodiments, the filtersegment comprises at least about 10 percent by weight of celluloseacetate.

In aerosol-generating articles in accordance with the present invention,the filter segment preferably comprises less than about 15 percent byweight of cellulose acetate.

In some embodiments, the filter segment comprises less than about 5percent by weight of cellulose acetate, preferably less than 3 percentby weight of cellulose acetate, more preferably less than 1 percent byweight of cellulose acetate, even more preferably less than 0.1 percentby weight cellulose acetate. This may favourable further contribute toenhance biodegradability of the filter segment and of theaerosol-generating article as a whole.

Preferably, an aerosol-generating article in accordance with the presentinvention comprises less than or equal to about 10 percent by weight ofcellulose acetate measured with reference to the overall weight of theaerosol-generating article. More preferably, an aerosol-generatingarticle in accordance with the present invention comprises less than orequal to about 7 percent by weight of cellulose acetate measured withreference to the overall weight of the aerosol-generating article. Evenmore preferably, an aerosol-generating article in accordance with thepresent invention comprises less than or equal to about 5 percent byweight of cellulose acetate measured with reference to the overallweight of the aerosol-generating article. This advantageously indicatesthat not only the filter segment has a low or null content of celluloseacetate, but also that any other component of the article containing afibrous filtration material contains little to no cellulose acetate.Embodiments of aerosol-generating articles in accordance with theinvention having such low contents of cellulose acetate presentparticularly favourable biodegradability properties.

In some preferred embodiments, an aerosol-generating article inaccordance with the present invention comprises less than or equal toabout 3 percent by weight of cellulose acetate measured with referenceto the overall weight of the aerosol-generating article. Morepreferably, an aerosol-generating article in accordance with the presentinvention comprises less than or equal to about 2 percent by weight ofcellulose acetate measured with reference to the overall weight of theaerosol-generating article. Even more preferably, an aerosol-generatingarticle in accordance with the present invention comprises less than orequal to about 1 percent by weight of cellulose acetate measured withreference to the overall weight of the aerosol-generating article.

In some highly preferred embodiments, an aerosol-generating article inaccordance with the present invention is substantially free of celluloseacetate.

In some embodiments, the filter segment further comprises at least about5 percent by weight of at least one biodegradable polymer selected fromthe group consisting of starch, polybutylene succinate (PBS),polybutyrate adipate terephthalate (PBAT), thermoplastic starch andthermoplastic starch blends (TPS), polycaprolactone (PCL), polyglycolide(PGA), polyvinyl alcohol (PVOH/PVA), viscose, regenerated cellulose,polysaccharides, cellulose acetate with a degree of substitution (DS) ofless than 2.1, polyamides, protein-based biopolymers, chitosan-chitinbased biopolymers, and combinations thereof. The inventors have foundthat including one or more of these ingredients in the blend from whichthe fibrous material of the filter segment is formed further contributesto enhancing biodegradability of the filter segment and of theaerosol-generating article as a whole.

In addition, while it has previously been found to be technicallychallenging to manufacture PHA-containing filaments or fibres, usingexisting techniques and apparatus, the inventors have surprisingly foundthat it is possible to produce a filaments or fibres incorporating ahigh level of PHAs when the PHAs are combined in a blend as describedabove, as this makes it easier to form the filaments by a spinningtechnique.

In preferred embodiments, the filter segment comprises at least about 10percent by weight of one such additional biodegradable polymer. Morepreferably, the filter segment comprises at least about 11 percent byweight or at least 12 percent by weight or at least 13 percent by weightor at least 14 percent by weight of the additional biodegradablepolymer. Even more preferably, the filter segment comprises at leastabout 15 percent by weight of one such additional biodegradable polymer.

In particularly preferred embodiments, the at least one biodegradablepolymer is one or more of PBAT, PCL and PBS. Without wishing to be boundby theory, the inventors have found that use of one or more of theseselected biodegradable polymers contributes to improving the mechanical,thermal and morphological properties of the polymer mix. In particular,use of PBAT and PBS in combination has been found to provide especiallywell balanced mechanical properties, especially in terms of tensilestrength and elongation.

In some embodiments, the fibrous filtration material comprises at leastabout 3 percent by weight of a plasticiser selected from triacetin,triethylene glycol diacetate (TEGDA), ethylene vinyl acetate, polyvinylalcohol, starch or combinations thereof.

In some embodiments, the fibrous filtration material also furthercomprises a water based adhesive. This has the effect of structurallyreinforcing the structure of the hollow tube segment. By way of example,compounds such as starch adhesive, methyl cellulose or polyvinyl acetatemay be used to this purpose.

Preferably, the fibrous filtration material of which the filter segmentis formed comprises a plurality of fibres comprising a PHA polymer orcopolymer and having a denier per filament of at least about 1. Morepreferably, the fibrous filtration material of which the filter segmentis formed comprises a plurality of fibres comprising a PHA polymer orcopolymer and having a denier per filament of at least about 2. Evenmore preferably, the fibrous filtration material of which the filtersegment is formed comprises a plurality of fibres comprising a PHApolymer or copolymer and having a denier per filament of at least about3.2.

In preferred embodiments, the fibrous filtration material of which thefilter segment is formed comprises a plurality of fibres comprising aPHA polymer or copolymer and having a denier per filament of less thanor equal to about 10. More preferably, the fibrous filtration materialof which the filter segment is formed comprises a plurality of fibrescomprising a PHA polymer or copolymer and having a denier per filamentof less than or equal to about 7.5. Even more preferably, the fibrousfiltration material of which the filter segment is formed comprises aplurality of fibres comprising a PHA polymer or copolymer and having adenier per filament of less than or equal to about 5.

In some embodiments, the fibrous filtration material of which the filtersegment is formed comprises a plurality of fibres comprising a PHApolymer or copolymer and having a denier per filament of from about 1 toabout 10, more preferably from about 2 to about 10, even more preferablyfrom about 3.2 to about 10. In other embodiments, the fibrous filtrationmaterial of which the filter segment is formed comprises a plurality offibres comprising a PHA polymer or copolymer and having a denier perfilament of from about 1 to about 7.5, more preferably from about 2 toabout 7.5, even more preferably from about 3.2 to about 7.5. In furtherembodiments, the fibrous filtration material of which the filter segmentis formed comprises a plurality of fibres comprising a PHA polymer orcopolymer and having a denier per filament of from about 1 to about 5,more preferably from about 2 to about 5, even more preferably from about3.2 to about 5.

Without wishing to be bound by theory, the inventors have found thatwhen the filter segment is formed with PHA fibres having a relativelylow DPF of between 1.5 and 3.2, the filter segment exhibits a relativelylow RTD, which may be desirable for the design of certain filters. Onesuch low range of DPF also advantageously reduces the overall weight ofthe filter segment, which further improves the biodegradability of theaerosol-generating article.

The transverse cross-sectional shape of the PHA fibres may be varied,for example, in order to control the external surface area of the fibreswithin the filter. By controlling the external surface area of the PHAfibres, the total surface area of the PHA fibres that is exposed to themainstream smoke as it passes through the filter segment may also becontrolled. This in turn will control to some extent the filtrationproperties of the PHA fibres, for example, the amount of water that isadsorbed by the fibres.

The total external surface area of the PHA fibres within the filtersegment is preferably between about 0.15 square metres per gram andabout 0.55 square metres per gram. (please add subranges).

The PHA fibres may have a substantially round cross-section. In suchembodiments, the total external surface area of the PHA fibres withinthe filter segment is preferably between about 0.15 square metres pergram and about 0.30 square metres per gram.

The PHA fibres may have a Y-shaped cross-section. In such embodiments,the total external surface are of the PHA fibres within the filtersegment is preferably between about 0.25 square metres per gram andabout 0.55 square metres per gram.

The PHA filter segment of the aerosol-generating articles according tothe invention may be adapted in order to provide a desired level ofresistance to draw (RTD). Advantageously, the PHA fibres can be arrangedto provide a relatively high RTD to the PHA filter segment. The PHAfilter segment is therefore particularly suitable for use in the filterof a combustible smoking article, where a relatively high RTD istypically desirable. Alternatively, the PHA filter segment may beparticularly suitable in aerosol-generating articles for which arelatively short mouthpiece or filter is preferred, since an acceptableRTD can still be provided.

Preferably, in aerosol-generating articles in accordance with thepresent invention an RTD of the PHA filter segment for a 27 millimetrefilter segment is at least about 25 millimetres H₂O. More preferably, anRTD of the PHA filter segment for a 27 millimetre filter segment is atleast about 50 millimetres H₂O, more preferably at least about 100millimetres H₂O. Even more preferably, in aerosol-generating articles inaccordance with the present invention an RTD of the PHA filter segmentfor a 27 millimetre filter segment is at least about 150 millimetresH₂O, more preferably at least about 180 millimetres H₂O. The RTD of thePHA filter segment for a 27 millimetre filter segment is preferably nomore than about 300 millimetres H₂O, more preferably no more than 250millimetres H₂O. For example, the RTD of the PHA filter segment for a 27millimetre filter segment may be between about 25 millimetres H₂O andabout 300 millimetres H₂O, or between about 50 millimetres H₂O and about300 millimetres H₂O, or between about 100 millimetres H₂O and about 250millimetres H₂O, or between about 150 millimetres H₂O and about 250millimetres H₂O, or between about 180 millimetres H₂O and about 250millimetres H₂O, or around 200 millimetres H₂O.

Preferably, in aerosol-generating articles in accordance with thepresent invention an RTD of the PHA filter segment (based on the lengthof the PHA filter segment in the article) is at least about 25millimetres H₂O. More preferably, an RTD of the PHA filter segment is atleast about 50 millimetres H₂O, more preferably at least about 100millimetres H₂O. Even more preferably, in aerosol-generating articles inaccordance with the present invention an RTD of the PHA filter segmentis at least about 150 millimetres H₂O, more preferably at least about180 millimetres H₂O. The RTD of the PHA filter segment (based on thelength of the PHA filter segment in the article) is preferably no morethan about 300 millimetres H₂O, more preferably no more than 250millimetres H₂O. For example, the RTD of the PHA filter segment may bebetween about 25 millimetres H₂O and about 300 millimetres H₂O, orbetween about 50 millimetres H₂O and about 300 millimetres H₂O, orbetween about 100 millimetres H₂O and about 250 millimetres H₂O, orbetween about 150 millimetres H₂O and about 250 millimetres H₂O, orbetween about 180 millimetres H₂O and about 250 millimetres H₂O, oraround 200 millimetres H₂O.

Preferably, in aerosol-generating articles in accordance with thepresent invention an RTD of the PHA filter segment (based on the lengthof the PHA filter segment in the article) is at least about 20millimetres H₂O. More preferably, an RTD of the PHA filter segment is atleast about 22 millimetres H₂O, more preferably at least about 25millimetres H₂O. Even more preferably, in aerosol-generating articles inaccordance with the present invention an RTD of the PHA filter segmentis at least about 28 millimetres H₂O, more preferably at least about 30millimetres H₂O. The RTD of the PHA filter segment (based on the lengthof the PHA filter segment in the article) is preferably no more thanabout 45 millimetres H₂O, more preferably no more than 40 millimetresH₂O. For example, the RTD of the PHA filter segment may be between about20 millimetres H₂O and about 45 millimetres H₂O, or between about 22millimetres H₂O and about 45 millimetres H₂O, or between about 25millimetres H₂O and about 40 millimetres H₂O, or between about 28millimetres H₂O and about 40 millimetres H₂O, or between about 30millimetres H₂O and about 40 millimetres H₂O, or around 37 millimetresH₂O.

“Resistance to draw” refers to the static pressure difference betweenthe two ends of a sample when it is traversed by an air flow understeady conditions in which the volumetric flow is 17.5 millilitres persecond at the output end. The RTD of a sample can be measured using themethod set out in ISO Standard 6565:2002.

The filter segment of the aerosol-generating articles according to theinvention may have a lower RTD compared to a filter segment of celluloseacetate fibres, which may be desirable for certain applications. Forexample, a relatively low RTD may be advantageous where a relatively lowfiltration efficiency is desirable or where a relatively long filter ispreferred.

The filter segment of the aerosol-generating article according to theinvention has additionally been found to provide a good stability in theRTD, which means that a high variability in the RTD can advantageouslybe avoided. For example, within a sample of 20 of the aerosol-generatingarticles according to the invention, there will typically be a standarddeviation from the target RTD of between 2 percent and 10 percent, morepreferably between 2 percent and 5 percent.

Preferably, the fibres comprising a PHA polymer or copolymer of thefilter segment are crimped.

In some embodiments, the filter segment may comprise one or moreadditive for reducing certain constituents in the mainstream smoke. Byway of example, the filter segment preferably comprises an additive forthe reduction of phenols and phenol derivatives. Suitable additiveswould be known to the skilled person and include, but are not limitedto: polyethylene glycol (PEG), triacetin, tri-ethyl citrate, celluloseacetate flakes or combinations thereof.

Preferably, the filter segment comprises between about 3 percent andabout 15 percent by weight of the additive, more preferably betweenabout 5 percent and about 9 percent by weight of the additive.

In certain preferred embodiments of the invention, the PHA filtersegment comprises polyethylene glycol, such as PEG 400.

The combination of PHA with an additive such as PEG for the reduction ofphenolic compounds from the mainstream smoke has been found to beparticularly effective. PHA fibres generally provide a good filtrationefficiency for undesirable smoke constituents but are less effective atthe removal of phenolic compounds. By incorporating a compound thatspecifically reduces the level of phenolic compounds in the mainstreamsmoke, it is possible to further optimise the filtration capabilities ofthe filter segment of an aerosol-generating article in accordance withthe invention. This in turn improves the sensory characteristics of theaerosol delivered to the consumer.

In particularly preferred embodiments, the filter segment furthercomprises at least about 5 percent by weight of polyethylene glycol,based on the total weight of the filtration material. Preferably, thefilter segment comprises no more than 10 percent by weight ofpolyethylene glycol, based on the total weight of the filtrationmaterial.

In other preferred embodiments of the invention, the PHA filter segmentfurther comprises a mixture of cellulose acetate and triacetin.Preferably, the mixture comprises at least 90 percent by weight oftriacetin and up to 10 percent by weight cellulose acetate. The mixturemay be formed by adding cellulose acetate flakes to triacetin to form asolution. The solution may then be sprayed onto the PHA fibres in thePHA filter segment. This combination has been found to advantageouslyreplicate the combined effects of triacetin and cellulose acetate fibresin the filter of a conventional cigarette.

As described above, it has been found that PHA fibres absorb less waterfrom the mainstream smoke than an equivalent amount of cellulose acetatefibres, due to the lower affinity of the PHA fibres to water. Asdemonstrated in the examples below, the amount of water absorbed by aPHA filter segment is significantly lower than the amount of waterabsorbed by a comparative filter segment formed of an equivalent weightof cellulose acetate fibres.

For example, when exposed to water in liquid form, the filter segment ofthe aerosol-generating article of the present invention preferablyabsorbs less than half the amount of water that is absorbed under thesame conditions by an equivalent filter segment formed of celluloseacetate fibres.

The reduced absorption of water by the PHA fibres in the filter segmentof the present invention, compared to cellulose acetate results in ahigher level of water in the mainstream smoke delivered from theaerosol-generating article during use.

For example, the amount of water in the mainstream smoke collectedduring the smoking of a combustible smoking article comprising a filteraccording to the invention with PHA fibres under ISO conditions was atleast 10 percent higher and preferably at least 15 percent higher thanthe amount of water in the mainstream smoke collected during the smokingof an equivalent combustible smoking article having a filter segment ofcellulose acetate tow under the same conditions.

Aerosol-generating articles comprising a filter including a PHA filtersegment are therefore able to deliver a mainstream smoke having a highermoisture level, which is more sensorially acceptable to the consumer. Inparticular, the ‘dry smoke’ effect that may be experienced duringsmoking of an aerosol-generating article with a conventional celluloseacetate filter can advantageously be reduced.

The fibres comprising a PHA polymer or copolymer of the filter segmentmay be manufactured by one of several techniques, including meltspinning, gel spinning, and electrospinning. Preferably, the fibrescomprising a PHA polymer or copolymer of the filter segment inaerosol-generating articles in accordance with the present invention aremanufactured by melt spinning. Melt spinning is often regarded as themost economical process of spinning, since no solvent needs to berecovered or evaporated, as is by contrast the case with solutionspinning. Further, the spinning rate with melt spinning is generallyfairly high, which is advantageous in terms of overall productivity andmanufacturing efficiency.

In this process, a viscous melt of polymer or of a polymer blend isextruded through a spinneret containing a number of holes into achamber, where a blast of cold air or gas is directed onto the surfaceof filaments emanating from the spinneret. As the air strikes thefilaments, the filaments are solidified and collected such as on atake-up wheel. The melt spinning process is advantageously characterisedby defined filament cross-section geometries and affords a significantvariety of fineness and filament count. By increasing the number ofopenings in the spinneret, a high spinning capacity can be achieved,which is difficult to match with other spinning processes.

In some embodiments, the filter segment may typically have a length ofat least about 4 millimetres. Preferably, a length of the filter segmentis at least about 5 millimetres. More preferably, a length of the filtersegment is at least about 7 millimetres. Even more preferably, a lengthof the filter segment is at least about 10 millimetres.

In such embodiments, the filter segment may typically have a length ofless than or equal to about 30 millimetres. Preferably, a length of thefilter segment is less than or equal to about 27 millimetres. Morepreferably, a length of the filter segment is less than or equal toabout 25 millimetres. Even more preferably a length of the filtersegment it less than or equal to about 20 millimetres.

In such embodiments, a length of the filter segment is preferably fromabout 5 millimetres to about 30 millimetres, more preferably from about10 millimetres to about 30 millimetres, even more preferably from about15 millimetres to about 30 millimetres, most preferably from about 20millimetres to about 30 millimetres. Alternatively, in such embodimentsa length of the filter segment may be from about 4 millimetres to about27 millimetres, and preferably is from about 5 millimetres to about 27millimetres, more preferably from about 10 millimetres to about 27millimetres, even more preferably from about 15 millimetres to about 27millimetres, most preferably from about 20 millimetres to about 27millimetres. As a further alternative, in such embodiments, a length ofthe filter segment may be from about 4 millimetres to about 25millimetres, and preferably is from about 5 millimetres to about 25millimetres, more preferably from about 10 millimetres to about 25millimetres, even more preferably from about 15 millimetres to about 30millimetres, most preferably from about 20 millimetres to about 25millimetres.

The filter segment preferably has an external diameter that is aboutequal to the external diameter of the aerosol-generating article.Preferably, the filter segment has an external diameter of at least 5millimetres. The filter segment may have an external diameter of betweenabout 5 millimetres and about 12 millimetres, for example of betweenabout 5 millimetres and about 10 millimetres or of between about 6millimetres and about 8 millimetres. In a preferred embodiment, thefilter segment has an external diameter of 7.2 millimetres, to within 10percent.

Preferably, in aerosol-generating articles in accordance with thepresent invention the filter segment has an average radial hardness ofat least 80 percent, more preferably at least 85 percent. The filtersegment is therefore able to provide a desirable level of filterhardness, which is comparable to that provided by a conventionalcellulose acetate tow filter. If desired, the radial hardness of thefilter segment of aerosol-generating articles in accordance with theinvention may be further increased by circumscribing the filter segmentby a stiff plug wrap, for example, a plug wrap having a basis weight ofat least about 80 grams per square metre (gsm), or at least about 100gsm, or at least about 110 gsm.

As used herein, the term “radial hardness” refers to resistance tocompression in a direction transverse to a longitudinal axis of thefilter segment. Radial hardness of an aerosol-generating article arounda filter may be determined by applying a load across the article at thelocation of the filter, transverse to the longitudinal axis of thearticle, and measuring the average (mean) depressed diameters of thearticles. Radial hardness is given by:

${{Radial}{hardness}(\%)} = {\frac{D_{d}}{D_{S}}*100\%}$

where D_(s) is the original (undepressed) diameter, and D_(d) is thedepressed diameter after applying a set load for a set duration. Theharder the material, the closer the hardness is to 100%.

To determine the hardness of a portion (such as a filter segment) of anaerosol article, aerosol-generating articles should be aligned parallelin a plane and the same portion of each aerosol-generating article to betested should be subjected to a set load for a set duration. This testis performed using a known DD60A Densimeter device (manufactured andmade commercially available by Heinr Borgwaldt GmbH, Germany), which isfitted with a measuring head for aerosol-generating articles, such ascigarettes, and with an aerosol-generating article receptacle.

The load is applied using two load-applying cylindrical rods, whichextend across the diameter of all of the aerosol-generating articles atonce. According to the standard test method for this instrument, thetest should be performed such that twenty contact points occur betweenthe aerosol-generating articles and the load applying cylindrical rods.In some cases, the filters to be tested may be long enough such thatonly ten aerosol-generating articles are needed to form twenty contactpoints, with each smoking article contacting both load applying rods(because they are long enough to extend between the rods). In othercases, if the filters are too short to achieve this, then twentyaerosol-generating articles should be used to form the twenty contactpoints, with each aerosol-generating article contacting only one of theload applying rods, as further discussed below.

Two further stationary cylindrical rods are located underneath theaerosol-generating articles, to support the aerosol-generating articlesand counteract the load applied by each of the load applying cylindricalrods.

For the standard operating procedure for such an apparatus, an overallload of 2 kg is applied for a duration of 20 seconds. After 20 secondshave elapsed (and with the load still being applied to the smokingarticles), the depression in the load applying cylindrical rods isdetermined, and then used to calculate the hardness from the aboveequation. The temperature is kept in the region of 22 degreesCentigrade±2 degrees. The test described above is referred to as theDD60A Test. The standard way to measure the filter hardness is when theaerosol-generating article have not been consumed. Additionalinformation regarding measurement of average radial hardness can befound in, for example, U.S. Published Patent Application PublicationNumber 2016/0128378.

In some embodiments, the filter segment described above is the onlysegment formed of filtration material forming a mouth end filter of theaerosol-generating article. In other embodiments, the aerosol-generatingarticle may comprise one or more additional filter segments formed offiltration material, which may be provided upstream or downstream of thefilter segment comprising a PHA polymer or copolymer as described above.For example, the filter segment comprising a PHA polymer or copolymermay be combined with one or more axially aligned filter plugs formed ofa fibrous filtration material, which may or may not includePHA-containing fibres. Alternatively or in addition, the filter segmentcomprising a PHA polymer or copolymer may be combined with one or moretubular elements, such as a tubular element formed of a fibrousfiltration material or a cardboard tube. Alternatively or in addition,the PHA filter segment may be combined with an aerosol-cooling element.

The filter segment of aerosol-generating articles according to theinvention may optionally comprise a flavourant. Flavourants can beincorporated using a variety of different means, which would be known tothe skilled person. For example, a flavourant may be incorporated in theform of a capsule which may be provided in the filter segment comprisinga PHA polymer or copolymer, or in an additional filter segment of theaerosol-generating article.

The filter segment of aerosol-generating articles according to theinvention is preferably circumscribed by an outer wrapper, for example,a tipping wrapper that circumscribes the filter segments, the downstreamend of the aerosol-generating substrate and any additional componentsthat may be provided in between. The tipping wrapper may comprise aremovable tipping wrapper portion, as described in WO-A-2017/162838.This enables at least a portion of the tipping wrapper to be removedbefore the aerosol-generating article is discarded. The removal of thetipping wrapper exposes the underlying filter segments and may thereforeadvantageously speed up the rate of biodegradation of the filtermaterials.

In some embodiments, an aerosol-generating article in accordance withthe present invention may further comprise one or more additionalelements that are typically assembled with the rod of aerosol-generatingsubstrate in a same wrapper. Examples of such additional elementsinclude a support element adapted to enhance the structural strength tothe aerosol-generating article, a cooling element adapted to favourcooling of the aerosol prior to reaching the filter segment, and soforth.

For example, in one preferred embodiment, an aerosol-generating articlecomprises, in linear sequential arrangement, a rod of aerosol-generatingsubstrate, a support element located immediately downstream of thesupport element, an aerosol-cooling element located downstream of thesupport element, and an outer wrapper circumscribing the rod, thesupport element, and the aerosol-cooling element. The rod, the supportelement, and the aerosol-cooling element are provided in lineararrangement and upstream of a filter segment as described above. In oneparticularly preferred embodiment, the rod, the support element, and theaerosol-cooling element are provided in linear arrangement andimmediately upstream of a filter segment as described above.

For example, a support element may be provided in the form of a tubularelement of a fibrous filtration material. The fibrous filtrationmaterial may comprise cellulose acetate. In preferred embodiments, thefibrous filtration comprises a polyhydroxyalkanoate (PHA) polymer orcopolymer.

In another preferred embodiment of the present invention, theaerosol-generating article comprises in a linear sequential arrangement:an aerosol-generating substrate, a transfer element, an aerosol-coolingelement, a spacer element and a filter segment as described above.

In certain preferred embodiments of the present invention, theaerosol-generating article further comprises a combustible heat sourceat the upstream end of the aerosol-generating article, in contact withthe upstream end of the aerosol-generating substrate. For example, theaerosol-generating article may comprise a carbonaceous heat source atthe upstream end, for heating the aerosol-generating substrate togenerate an aerosol during use. Suitable carbonaceous heat sources wouldbe known to the skilled person.

The invention will now be further described with reference to thefigures in which:

FIG. 1 shows a schematic longitudinal cross-sectional view of anaerosol-generating article according to a first embodiment of theinvention, for use with an aerosol-generating device comprising a heaterelement;

FIG. 2 shows a schematic longitudinal cross-sectional view of anaerosol-generating article according to a second embodiment of theinvention, comprising an integral heat source; and

FIG. 3 shows a schematic longitudinal cross-sectional view of anaerosol-generating article according to a third embodiment of theinvention;

FIG. 4 shows a schematic longitudinal cross-sectional view of anaerosol-generating system comprising an electrically operatedaerosol-generating device and the aerosol-generating article shown inFIG. 1 .

The aerosol-generating article 10 shown in FIG. 1 comprises a rod ofaerosol-generating substrate 12, a support element provided as a hollowtubular element 14, a cooling element 16, and a mouth end filter segment18. These four elements are arranged sequentially and in coaxialalignment and are circumscribed by a substrate wrapper 20 to form theaerosol-generating article 10. The aerosol-generating article 10 has amouth end 22 and a distal end 24 located at the opposite end of thearticle to the mouth end 22. The aerosol-generating article 10 shown inFIG. 1 is particularly suitable for use with an electrically operatedaerosol-generating device comprising a heater for heating the rod ofaerosol-generating substrate.

In use air is drawn through the aerosol-generating article by a userfrom the distal end 24 to the mouth end 22. The distal end 24 of theaerosol-generating article may also be described as the upstream end ofthe aerosol-generating article 10 and the mouth end 22 of theaerosol-generating article 10 may also be described as the downstreamend of the aerosol-generating article 10. Elements of theaerosol-generating article 10 located between the mouth end 22 and thedistal end 24 can be described as being upstream of the mouth end 22 or,alternatively, downstream of the distal end 24.

The aerosol-generating substrate 24 is located at the extreme distal orupstream end of the aerosol-generating article 10. In the embodimentillustrated in FIG. 1 , the aerosol-generating substrate 12 comprises agathered sheet of crimped homogenised tobacco material circumscribed bya wrapper. The crimped sheet of homogenised tobacco material comprisesglycerin as an aerosol former.

The support element 14 is located immediately downstream of theaerosol-generating substrate 12 and abuts the aerosol-generatingsubstrate 12. In the embodiment shown in FIG. 1 , the support element isa hollow tube formed of a fibrous filtration material. The supportelement 14 locates the aerosol-generating substrate 12 at the extremedistal end 24 of the aerosol-generating article 10 so that it can bepenetrated by a heating element of an aerosol-generating device. Ineffect, the support element 14 acts to prevent the aerosol-generatingsubstrate 16 from being forced downstream within the aerosol-generatingarticle 10 towards the aerosol-cooling element 16 when a heating elementof an aerosol-generating device is inserted into the aerosol-generatingsubstrate 12. The support element 14 also acts as a spacer to space theaerosol-cooling element 16 of the aerosol-generating article 10 from theaerosol-generating substrate 12.

The aerosol-cooling element 16 is located immediately downstream of thesupport element 14 and abuts the support element 16. In use, volatilesubstances released from the aerosol-generating substrate 12 pass alongthe aerosol-cooling element 16 towards the mouth end 22 of theaerosol-generating article 10. The volatile substances may cool withinthe aerosol-cooling element 16 to form an aerosol that is inhaled by theuser. In the embodiment illustrated in FIG. 1 , the aerosol-coolingelement comprises a tubular element 20. The crimped and gathered sheetof polylactic acid defines a plurality of longitudinal channels thatextend along the length of the aerosol-cooling element 40.

The filter segment 18 is located immediately downstream of theaerosol-cooling element 16 and abuts the aerosol-cooling element 16. Inthe embodiment illustrated in FIG. 1 , the filter segment 18 comprises asingle cylindrical plug of a fibrous filtration material formed of aplurality of PHA fibres having a denier per filament of approximately 3and a total denier of approximately 27,000. The PHA fibres have a roundcross-sectional shape and are substantially longitudinally aligned witheach other along the length of the filter segment. The exposed surfacearea of the PHA fibres corresponds to about 0.16 square metres per gram.The PHA fibres have been formed by a melt spinning process and arecrimped. In more detail, the fibres contain about 85 percent by weightof a PHA polymer or copolymer combined with 15 percent by weight of a ofPBAT/PBS blend with a 1:1 PBAT to PBS ratio. The plug of fibrousfiltration material is circumscribed by a plug wrap (not shown).

The aerosol-generating article 100 shown in FIG. 2 comprises acombustible heat source 112, a rod of aerosol-generating substrate 114,a transfer element 116, an aerosol-cooling element, 118, a spacerelement 120 and a mouthpiece filter segment 122. These elements arearranged sequentially and in coaxial alignment and are circumscribed bya substrate wrapper to form the aerosol-generating article 100.

The combustible heat source 112 comprises a substantially circularlycylindrical body of carbonaceous material, having a length of about 10millimetres. The combustible heat source 112 is a blind heat source. Inother words, the combustible heat source 112 does not comprise any airchannels extending therethrough.

The rod of aerosol-generating substrate 114 is arranged at a proximalend of the combustible heat source 112. The aerosol-generating substrate114 comprises a substantially circularly cylindrical plug of tobaccomaterial 124 circumscribed by filter plug wrap 126.

A non-combustible, substantially air impermeable first barrier 128 isarranged between the proximal end of the combustible heat source 112 anda distal end of the aerosol-generating substrate 114. The first barrier128 comprises a disc of aluminium foil. The first barrier 128 also formsa heat-conducting member between the combustible heat source 112 and theaerosol-generating substrate 114, for conducting heat from the proximalface of the combustible heat source 112 to the distal face of theaerosol-generating substrate 114.

A heat-conducting element 130 circumscribes a proximal portion of thecombustible heat source 112 and a distal portion of the aerosol-formingsubstrate 114. The heat-conducting element 130 comprises a tube ofaluminium foil. The heat-conducting element 130 is in direct contactwith the proximal portion of the combustible heat source 112 and thefilter plug wrap 126 of the aerosol-generating substrate 114.

The mouthpiece filter 122 comprises a single cylindrical plug 126 of afibrous filtration material formed of a plurality of PHA fibres having adenier per filament of approximately 3 and a total denier ofapproximately 27,000. The PHA fibres have a round cross-sectional shapeand are substantially longitudinally aligned with each other along thelength of the filter segment. The exposed surface area of the PHA fibrescorresponds to about 0.16 square metres per gram. The PHA fibres havebeen formed by a melt spinning process and are crimped. The plug offibrous filtration material is circumscribed by a plug wrap (not shown).

The aerosol-generating article 310 shown in FIG. 3 is a combustiblesmoking article comprising an aerosol-generating substrate 312 and afilter 314 arranged in coaxial alignment with each other. Theaerosol-generating substrate 312 comprises a tobacco rod circumscribedby an outer wrapper (not shown). A tipping wrapper 316 circumscribesboth the filter 314 and an end portion of the aerosol-generatingsubstrate 312 and attaches the filter 314 to the aerosol-generatingsubstrate 312.

The filter 314 comprises a single cylindrical plug 318 of a fibrousfiltration material formed of PHA fibres having a denier per filament ofapproximately 3 and a total denier of approximately 27,000. The PHAfibres have a round cross-sectional shape and are substantiallylongitudinally aligned with each other along the length of the filtersegment. The exposed surface area of the PHA fibres corresponds to about0.16 square metres per gram. The PHA fibres have been formed by a meltspinning process and are crimped. The plug of fibrous filtrationmaterial is circumscribed by a plug wrap (not shown).

FIG. 4 shows a portion of an electrically operated aerosol-generatingsystem 200 that utilises a heater blade 210 to heat the rod ofaerosol-generating substrate 12 of the aerosol-generating article 10shown in FIG. 1 . The heater blade 210 is mounted within anaerosol-generating article chamber within a housing of an electricallyoperated aerosol-generating device 212. The aerosol-generating device212 defines a plurality of air holes 214 for allowing air to flow to theaerosol-generating article 10, as illustrated by the arrows in FIG. 4 .The aerosol-generating device 212 comprises a power supply andelectronics, which are not shown in FIG. 4 .

COMPARATIVE EXAMPLE

[Incorporate Discussion of Tests 1 and 2 from IDR?]

A PHA filter segment according to the invention was prepared from PHAfibres, with the parameters shown in Table 1 below. The PHA fibres wereformed using a melt spinning process, the fibres were then crimped andformed into a filter segment using standard filter making apparatus. Forthe purposes of comparison, a conventional cellulose acetate (CA) towfilter segment was prepared, with similar values of denier per filament(dpf) and total denier.

TABLE 1 parameters of PHA filter segment and cellulose acetate filtersegment PHA filter CA filter Parameter segment segment Denier perfilament 3.2 3 Total denier 27000 27000 Weight in filter segment (mg)406.76 409.76 Exposed surface area (m²/g) 0.161 0.329

In a first test, the water absorption by exposure to water of the PHAfilter segment according to the invention and the CA filter segment werecompared. For each filter segment, the plug wrap was removed and thefilter segment was attached to the probe of a force tensiometer (KRUSSforce tensiometer, Model K100). The filter segment is moved down by theprobe towards a container of water and automatically stopped when thefilter segment makes contact with the water. The filter segment isretained in contact with the water for 300 seconds so that the filtermaterial can absorb water and then the filter segment is weighed inorder to determine the amount of water absorbed during the test period.For each of the PHA filter segment and the CA filter segment, this testwas repeated three times and an average value of water absorption wascalculated, as shown below in Table 2:

TABLE 2 Water absorption of the PHA and CA filter segments afterexposure to water PHA filter CA filter segment segment Water absorptionin 300 sec (g) 0.51 1.37

The amount of water absorbed by the PHA filter segment according to theinvention during the test was therefore less than 40 percent of theamount of water absorbed by the CA filter segment. This test thereforedemonstrates the significantly reduced affinity of water of the PHAfilter segment according to the invention compared to the conventionalCA filter segment.

In a second test, the water absorption by exposure to moisture of thePHA filter segment according to the invention and the CA filter segmentwere compared. For each filter segment, the plug wrap was removed andthe fibres forming the filter segment were placed in a petri dish andexposed to air at 22 degrees Celsius and 50 percent relative humidityfor 70 hours. This was conducted in a vapour sorption analyser (ProUmidSPSx-1μ). For each filter segment, the weight of the fibres is measuredat the start of the test and the change in weight over time due to theabsorption of water vapour by the fibres is measured. For each of thePHA filter segment and the CA filter segment, a value of the percentagedifference in mass of the sample (% dm) was calculate, which expressesthe increase in the weight of the sample as a percentage of the originalweight. The values of % dm for each of the samples at the end of the 70hour test are shown below in Table 3:

TABLE 3 Water absorption of the PHA and CA filter segments afterexposure to moisture PHA filter CA filter segment segment % Differencein mass after 0.0133 0.6784 70 hours (% dm)

The results demonstrate that the amount of water vapour absorbed by thecellulose acetate fibres during the 70 hour test was more than 50 timesgreater than the amount of water vapour absorbed by the PHA fibres. ThePHA fibres absorbed very little water vapour during the test. Thisfurther demonstrates the significantly reduced affinity of water of thePHA filter segment according to the invention compared to theconventional CA filter segment.

In a third test, the absorption of water from the mainstream smoke by aPHA filter segment according to the present invention and a conventionalCA filter segment were compared. For each of the filter segments, aconventional smoking article was prepared as described above withreference to FIG. 3 , with a combustible tobacco rod and a singlesegment of the filtration material forming the filter. Each of thesmoking articles was then smoked in a cigarette-smoking machine underISO conditions as set out in ISO 3308:2000 (puff volume 35 ml; 2 secondpuff duration every 60 seconds) and an analysis of the resultant smokewas carried out. For each of the filter segments, the amount of water inthe mainstream smoke collected during the smoking test was measured, asshown in Table 4:

TABLE 4 Water in mainstream smoke generated during smoking test underISO conditions PHA filter CA filter segment segment Water (mg persmoking article) 0.82 0.68

This demonstrates that when smoked under equivalent conditions, thesmoking article incorporating the PHA filter segment produces amainstream smoke having a water content that is approximately 20 percenthigher than the water content of the mainstream smoke from the smokingarticle including the CA filter segment. This demonstrates that the PHAfilter segment is absorbing less water from the mainstream smoke thanthe CA filter segment, thereby reducing the potential problem of drysmoke as described above.

1.-15. (canceled)
 16. An aerosol-generating article for producing aninhalable aerosol upon heating, the aerosol-generating articlecomprising: a rod of aerosol-generating substrate, theaerosol-generating substrate comprising at least 10 percent by weight ofan aerosol former; and a filter segment formed of fibrous filtrationmaterial, the filter segment arranged in longitudinal alignment with therod, wherein the filter segment comprises at least about 85 percent byweight based on a total weight of fibrous filtration material of apolyhydroxyalkanoate (PHA) polymer or copolymer, wherein a resistance todraw (RTD) of the filter segment is between about 35 millimetres H₂O andabout 55 millimetres H₂O, and wherein a length of the filter segment isfrom about 4 millimetres to about 27 millimetres.
 17. Theaerosol-generating article according to claim 16, wherein the filtersegment further comprises at least about 90 percent by weight based onthe total weight of fibrous filtration material of thepolyhydroxyalkanoate (PHA) polymer or copolymer.
 18. Theaerosol-generating article according to claim 16, wherein the filtersegment further comprises at least about 95 percent by weight based onthe total weight of fibrous filtration material of thepolyhydroxyalkanoate (PHA) polymer or copolymer.
 19. Theaerosol-generating article according to claim 16, wherein the filtersegment further comprises at least about 5 percent by weight based onthe total weight of fibrous filtration material of at least onebiodegradable polymer selected from the group consisting of starch,polybutylene succinate (PBS), polybutyrate adipate terephthalate (PBAT),thermoplastic starch and thermoplastic starch blends (TPS),polycaprolactone (PCL), polyglycolide (PGA), polyvinyl alcohol(PVOH/PVA), viscose, regenerated cellulose, polysaccharides, celluloseacetate with a degree of substitution (DS) of less than 2.1, polyamides,protein-based biopolymers, chitosan-chitin based biopolymers, andcombinations thereof.
 20. The aerosol-generating article according toclaim 19, wherein the filter segment further comprises at least about 10percent based on the total weight of fibrous filtration material of theat least one biodegradable polymer.
 21. The aerosol-generating articleaccording to claim 19, wherein the filter segment further comprises lessthan or equal to about 15 percent by weight based on the total weight offibrous filtration material of the at least one biodegradable polymer.22. The aerosol-generating article according to claim 19, wherein the atleast one biodegradable polymer is one or more of PBAT, PCL, and PBS.23. The aerosol-generating article according to claim 16, wherein thefibrous filtration material comprises a plurality of fibres comprising apolyhydroxyalkanoate (PHA) polymer or copolymer and having a denier perfilament from about 1 to about
 10. 24. The aerosol-generating articleaccording to claim 16, wherein the fibrous filtration material comprisesa plurality of fibres comprising a polyhydroxyalkanoate (PHA) polymer orcopolymer and having a denier per filament from about 3.2 to about 5.25. The aerosol-generating article according to claim 16, wherein an RTDof the filter segment is between about 40 millimetres H₂O and about 50millimetres H₂O.
 26. The aerosol-generating article according to claim16, wherein the fibrous filtration material comprises crimped fibrescomprising a polyhydroxyalkanoate (PHA) polymer or copolymer.
 27. Theaerosol-generating article according to claim 16, wherein a diameter ofthe filter segment is from about 5 millimetres to about 12 millimetres.28. A filter for an aerosol-generating article, the filter comprising: afilter segment formed of fibrous filtration material, the filter segmentcomprising at least about 85 percent by weight based on a total weightof fibrous filtration material of fibres comprising apolyhydroxyalkanoate (PHA) polymer or copolymer, wherein a resistance todraw (RTD) of the filter segment is between about 35 millimetres H₂O andabout 55 millimetres H₂O, and wherein a length of the filter segment isfrom about 4 millimetres to about 27 millimetres.